This invention relates to magnetic tape storage and accessing systems for tape libraries, for example, or for backup storage of digital information.
Tape libraries are known in the field as indicated by U.S. Pat. No. 5,498,116, granted Mar. 12, 1996, and as disclosed in U.S. patent application Ser. No. 08/427,884, filed Apr. 26, 1995, and assigned to the assignee of this invention. In these systems, a large number of tape cassettes or cartridges are stored in tower-like configurations, and transfer mechanisms are provided for selecting designated tape cassettes and transporting them to a tape drive where data may be accessed from the tape cassettes or written into the tape cassette or cartridge.
One disadvantage of these known prior art arrangements is that they take up more space than is desirable. Thus, for example, standard electronic racks for mounting electronic equipment are normally 19 inches wide and have vertical spaces for storing electronic equipment in, in terms of standard increments or units of height equal to one and three quarters (1xc2xe) inches. Electronic equipment intended for rack mounting is normally designed to occupy a predetermined number of units of height, such as one unit of height (1xc2xe inches) or two or three units of height (3xc2xd inches or 5xc2xc inches respectively).
If the prior art tape library systems as identified above were to be mounted in standard electronic racks, they would occupy a large number of units of height, such as at least five or ten units of height, and this would be considered very wasteful of available rack space.
Accordingly, a principal object of the invention is to provide a magnetic tape cassette or cartridge storage and accessing system which is compact and which is compatible with standard electronic rack dimensions.
In accordance with one illustrative embodiment of the invention, the tape cassette storage and accessing system includes a linearly extending frame, with two sides, and link chains mounted respectively on the two sides, with tape cassette or cartridge carriers having linkages interconnecting one end of each cassette carrier to both chains, and with each of the chains extending in a closed loop between the front and rear of the frame, with the upper portion of each chain being substantially parallel to the lower portion and with the two sections of chain being spaced apart by a distance which is slightly greater than the thickness of the carriers when loaded with cassettes. The cassette carriers are mounted to said chains in two layers with the upper layer moving in one direction and the lower layer moving in the opposite direction, and with each layer including a plurality of cassette carriers. Each cassette carrier may also have at least one cam follower for engaging grooves in one or both sides of the frame, for guiding the carriers and for tilting the carriers at the two ends of the frame to smoothly shift the cassette carriers from one of the layers of carriers to the other layer.
Concerning other aspects of the invention, it may involve the following factors:
(1) Instead of a link chain, a toothed belt or a continuous flexible line may be used.
(2) At the front and/or the rear of the frame, a movable guide and latch may be provided for positively controlling shifting of the carriers from one layer to the other.
(3) Instead of a cam follower and groove, the sides of the frame may be provided with a ridge or rib engaged by a forked cam follower or the cassette carrier.
(4) The system may be provided with an electromagnetic actuator for positively shifting the carriers from one layer to the other instead of the guide and latch arrangements.
(5) The cassette or cartridge carriers may be in the form of open trays, or may have structure enclosing the cassettes on both of the broader sides of the cassettes.
The design as described herein above may be employed with 8 mm tape cartridges and is successful in achieving a height of one unit, or one and three-quarters inches, for an electronic rack mounted unit. This is considered to be a surprising accomplishment when two 8 mm tape cassettes stacked on top of one another have a height of 1xe2x85x9 or 1{fraction (3/16)} inches. In this space of 1xc2xe inches of height, 17xc2xe of width and a depth of about two feet, a complete tape library may be contained, giving access to any of twenty-four 8 mm magnetic tape cassettes, with the cassettes being mounted with two cassettes side by side on each carrier, and with two layers of six carriers each.
Other objects, features and advantages of the invention will become apparent from the following detailed description and from the accompanying drawings.